In the chemical reaction below, calcium metal and water react to form calcium hydroxide and hydrogen gas.

Question

calcium metal + water → calcium hydroxide + hydrogen gas

Calcium and water are the reactants in this chemical reaction, whereas calcium hydroxide and hydrogen gas are the products that are formed. Once the reaction reaches completion,
A.
the total mass of the products will be equal to the original mass of the reactants.
B.
the total mass of the products will be greater than the original mass of the reactants.
C.
the products of the reaction will have changed back into the reactants.
D.
the total mass of the products will be less than the original mass of the reactants.

Answer 1

In a chemical reaction, according to the law of conservation of mass, the total mass of the reactants must equal the total mass of the products. This means that the mass is neither created nor destroyed during the reaction; it is just transformed from reactants into products.

Given the reaction you outlined:

Calcium metal + Water → Calcium hydroxide + Hydrogen gas

Once the reaction reaches completion, the correct answer is:

A. the total mass of the products will be equal to the original mass of the reactants.

This is due to the principle of conservation of mass, which states that in a closed system, the mass remains constant throughout the reaction.